1. Field of the Invention
The present invention relates to bearing members, and, in particular, cylinders have an inner bearing surface, and relates to a method of making such a cylinder.
2. Description of the Related Art
Cylinders having an inner bearing surface are well known in the art for use in hydraulic applications. Such cylinders have typically been made of, e.g., aluminum or steel.
Potential seal wear is a significant issue to consider with respect to cylinders. As discussed in “Variseal Design Guide” by American Variseal, two characteristics account for a majority of dry-contact friction between mating parts: adhesion and interlocking. As the area of contact between two surfaces increases, adhesion therebetween can also increase. Consequently, a smoother surface finish tends to promote greater contact and, thus, greater adhesion between adjoining surfaces.
Interlocking, conversely, is a product of the presence of surface irregularities on at least one of two adjoining surfaces, the peaks of such irregularities tending to shear when another surface is slid thereover. When a hard, rough surface is engaged with a softer material the peaks of the harder material tend to penetrate into the surface of the softer material, resulting in interlocking friction therebetween. Thus, to minimize friction, adjoining surfaces should be smooth enough so as to have little or no surface irregularities to reduce the potential for interlocking therebetween yet not be so smooth so as to significantly promote adhesion therebetween.
Current technology employs a gel coat to provide a smooth bore surface in composite pneumatic and hydraulic cylinders. However, there are various drawbacks associated with the use of such a gel coat. First, since such a gel coat is usually applied via spraying, volatile matter is typically a by-product that must be accounted for and cost becomes a concern as spraying processes can be expensive, especially if volatile matter need be recovered. Furthermore, gel-coated bores tend to have a significant coefficient of friction associated therewith, even though lower than that of untreated bores. Additionally, tests have shown after being exposed to a high number of cyclings (e.g., 1 million), gel-coated cycles can have a considerable amount of fairly hard, gum-like material developed in the seal region. Other tests have shown that after even 100,000 cycles, a gel coat on a bore can show signs of cracking and blistering.
What is needed in the art is a bearing cylinder with an optimized inner bore finish that is both as rough and hard (i.e., wear resistant) as possible, and that will not “dig” into any adjoining part while still meeting maximum leakage and wear requirements.